Access value of struct data member from other file-CodePudding

I have a data member in computer.h called "status" that I calculate a value for in computer.c. I would like to access this exact value and print it in a different file called display.c.

The problem is I'm not exactly sure how I can access that variable. I'm not allowed to change the parameters of display_status() and I'm assuming creating a new computer_data struct to access the status member in that function will just create a new local variable and won't work.

I'm not exactly sure how I can access the value of computer_data->status in display.c and would appreciate any help. Would I create a getter function for status specifically or something?

computer.h

struct computer_data {
    struct param *status;
}

computer.c

static void computer_assign_status(){

    struct computer_data *computer = computer_get_data();

    computer->status = calculateStat();
}

display.c

#include "computer.h"

void display_status(){

    struct computer_data *computer = computer_get_data();
    
    printf("computer->status: %d /n", computer->status);

}

Note: Also computer_get_data() as a function is defined as "struct computer_data *computer_get_data()"

CodePudding user response：

Using a get function is a good start. You just have to make it known in the other file.

In computer.h add a declaration:

struct computer_data {
    struct param *status;
}

struct computer_data *computer_get_data(void);

Then you can use it in display.c.

But, of course for printing status you cannot use %d format specifier as it is a pointer to a struct.

Also in computer.c you have an error:

struct void computer_assign_status(){

That should just be void as return type.

Would I create a getter function for status specifically or something?

This totally depends on your needs. If you want to hide everything else that might be in that struct from a caller, then you might provide a function only returning pointer to the status part. Otherwise you can just do it as now where you return pointer to whole data struct.

CodePudding user response：

None of your examples accesses any data defined in another compilation unit. BTW your examples are written sloppy: as an example struct void. Put some more effort when asking questions here

You can only access global (more precisely static storage with external linkage) variables defined in other compilation units.

in computer.h

struct computer_data {
    struct param *status;
}

extern struct computer_data computer;

in computer.c

#include "computer.h"

struct computer_data computer;

void computer_assign_status(void)
{
    computer.status = calculateStat();
}

in display.c

#include "computer.h"

void display_status()
{
    printf("computer->status: %d /n", computer.status);
}

CodePudding user response：

In display.c do:

extern struct computer_data * computer = computer_get_data()

instead.

This works because with the extern keyword the compiler you're using will be forced to look for the variable in an external file.